Bhagavad Gita gives the dualistic worship of "God” only for the lower minds; it also teaches Advaita for the more evolved.
Likewise thinkers and poets of the Age of Devotion (Bhakti) of the 16th century believed in a God with attributes who became very tangible when incarnating as Avatar, and was attainable simply through love and devotion rather than scholastic and intellectual meditation.
For the religious people the Bhagavad Gita became the main vehicle of inspiration with its qualified and deistic Monism, rather than the scholastic and esoteric path shown by Sage Sri, Sankara’s Advaitic path.
Devotional prayer (Bhakti) value only for the ignorant who believe the world in which they are born is real. But for the seeker on his journey to the ultimate realization of the truth beyond the form time and space the devotional path becomes an obstacle.
People worship God in various ways, not knowing the Truth. At different levels, at different epochs, in different lands, people have different conceptions of God. They have quarreled because they did not know the truth about God.
The conflict of opinions among mystics and religionists proves that all are imagining God as they like, not knowing God.
Rig Veda: ~ The Atman (Soul or Spirit) is the cause; Atman is the support of all that exists in this universe. May ye never turn away from the Atman the innermost self. May ye never accept another God in place of the Atman nor worship other than the Atman?" (10:48, 5)
Rig-Veda 1-164-46 and Y.V 32-1 clearly mention that God is “One”.
Rig Veda declares God is ‘ONE’ and God is Atman, then why believe and worship in place of real God.
Brihad Upanishad: ~ “If you think there is another entity, whether man or God there is no truth."
When Upanishad itself declares: ~ Sarvam khalvidam brahma ~ all this (universe) is verily Brahman. By following back all of the relative appearances in the world, we eventually return to that from which it is all manifest – the non-dual reality (Chandogya Upanishad).
Sage Sri, Sankara’s Supreme Brahman (God) is impersonal, Nirguna (without Gunas or attributes), Nirakara (formless), Nirvisesha (without special characteristics), immutable, eternal and Akarta (non-agent). It is above all needs and desires. It is always the Witnessing Subject. It can never become an object as It is beyond the reach of the senses. Brahman is non-dual, one without a second. It has no other beside it. It is destitute of difference, either external or internal. Brahman cannot be described because description implies distinction. Brahman cannot be distinguished from any other than It. In Brahman, there is not the distinction of substance and attribute. Sat-Chit-Ananda constitutes the very essence or Svarupa of Brahman, and not just Its attributes. The Nirguna Brahman of Sage Sri, Sankara is impersonal.
Sage Sri, Sankara: ~"That which permeate~"That which permeates all, which nothing transcends and which, like the universal space around us, fills everything completely from within and without, that Supreme non-dual Brahman (God)."
Thus, truth realization is self-realization. The Self-realization is God realization. God -realization is real worship.